Daniel and Kelly’s Extraordinary Universe - How do LEDs work?

Episode Date: May 7, 2020

The Nobel-prize winning physics of.... reading lights. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

This is an I-Heart podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System

On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone.

Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hi, it's Honey German, and I'm back with season two of my podcast. Grazias, come again. We got you when it comes to the latest in music and entertainment with interviews with some of your favorite Latin artists and celebrities. You didn't have to audition? No, I didn't audition. I haven't auditioned in like over 25 years.

Oh, wow. That's a real G-talk right there. Oh, yeah. We'll talk about all that's viral and trending with a little bit of cheesement and a whole lot of laughs. And of course, the great bevras you've come to expect. Listen to the new season of Dresses Come Again on the Iheart Radio app, Apple Podcast,

or wherever you get your podcast. Hey, Daniel, I have a question about Nobel Prizes. Well, you know, they aren't awarded until much later this year, so don't stay up late and wait by your phone. Oh, really? They don't give one for podcasts? No, and they also don't give a banana prize. Well, my question is about the physics Nobel Prize. Well, I'm not staying up late and waiting by the phone either. Well, my question is whether it's given to some discovery that is deep or a discovery that's useful to humanity.

Why does it have to be one or the other? Isn't deep knowledge also useful? Have you found neutrinos to be useful to humanity? Not yet, actually. I'm still waiting for aliens to teach us how to use neutrinos to get a safe tan. Yeah, don't wait by the phone for that. Sweden, call me. Jupiter, call me. What does that even mean?

If there are aliens in Jupiter, I want the Joviant Nobel Prize for Best Podcast Sidekick. Wait, you're not the sidekick. I'm the sidekick. What? What? I am Jorge. I'm a cartoonist and the creator of Ph.D. Comites. Hi, I'm Daniel. I'm a particle physicist. And until a moment ago, I thought I was the sidekick on this podcast. And so welcome to our podcast, the award-winning science and physics podcast called Daniel and Jorge, Explain the Universe. Remind me which award we won? We won the award for having no awards yet.

The award for Best Podcasts that features only two sidekicks. We're sidekicking it here on our podcast. But yeah, it's our podcast about physics and science and astronomy and the universe and everything in between. Our podcast in which we share with you the gorgeous, amazing mysteries of the universe. We take you on a mental tour to all the crazy stuff that's out there that's in here, the tiny stuff, the huge stuff. And we explain it all to you in a way that we hope also makes you chuckle. Yeah, because, you know, we hope to open up your mind to the amazing, and incredible things that are happening right now

in the far reaches of the universe and the far corners of the solar system, but we also kind of want to open your eyes to see all of the amazing signs that's happening all around you right now. Because one of the most amazing things about physics is that the same laws of physics operate on black holes

and nebula and neutron stars and you and me and everything in our world. This is one of the most earth-shattering revelations of physics in the last few hundred years that the physics of the cosmos and the physics of the everyday are the same physics, which means that we can discover the secrets of the universe just by doing

experiments in our laboratory. Yeah, it's all the same, being trapped in a black hole or being trapped in your apartment for an indefinite amount of time. It's all the same. You can do physics anywhere. They're crushing in different ways. But it also means that we can look around us and find amazing, crazy

stuff that reveals secrets of the universe. Like quantum mechanics was not discovered inside a black hole. It was found just by shooting photons, at weird kinds of metal. And so today we'll be talking about an invention that I would argue maybe is one of the most commonplace or most prevalent technologies out there in human technology, humankind, right? Are you talking about the wheel?

Fire? The hoverboard. I was hoping for the hoverboard. Hasn't that happened yet, Daniel? No, it is not. But I'm sure somebody accidentally ordered a hoverboard on Amazon and got something else, you know. Well, it's a technology that I think basically almost every human looks at on a daily basis. maybe even an hourly basis.

Now you have me at the edge of my seat. What are we talking about today? What do you mean? I thought you knew what we were talking about today. I'm the sidekick here, remember? You're in charge. Oh, I see. I see.

Well, it's in our phones. You know, everyone looks at their phone every couple of minutes. It's on our computer screens and our televisions, which I'm sure a lot of people are watching a lot of these days. So it illuminates everything. You're talking about my sheer genius, right? My brilliance. Talk about Netflix.

No, I'm just kidding. Well, I just figured out it's on the title of our. podcast. So I'm guessing that people will already know by the time they click on it. That's right. I hope they haven't been misled. That's right. We'll lead him to the light. That's right. So today on the podcast, we'll be talking about LEDs. How do LEDs work? What are the physics of it?

And why did somebody win a Nobel Prize for inventing a particular color of it? That's right. We have physics Nobel Prizes for things like understanding quantum mechanics and figuring out what the basic particles are or for, you know, an observation of gravitational waves, things that reveal the fundamental fabric in nature of the universe. And then we have Nobel Prizes for the invention of the blue LED. The blue LED, not the red LED. That one did not win. No, no. Was blue Nobel's favorite color? Not at all. Not at all. And so today we wanted to dive into like, what are the physics of LEDs?

Is this really worth a Nobel Prize? What are the sort of obstacles that they had to leap over in order to make this thing work? And what physics did they have to solve along the way? What does it reveal about the nature of our universe that we can now make LEDs glow blue? So what do you think about my idea that it's maybe one of the most prevailing technologies out there? You mean lights in general or LED specifically? LED specifically, you know? Because they're basically in every phone and there's billions of phones out there.

And it's on every computer screen now, in TV screens. Most TV screens have them. I would say it's up there along with concrete and toilet paper as the current most important technology. Yeah, you know, people have been stockpiling LEDs ever since the coronavirus came out, you know, just in case they run out.

Yeah, you know, just in case we run out of lights. I think you're right. It's had a really big impact on everyday life. You see them in screens. You see them in lights. You see them on trucks. You see them everywhere now. Yeah, yeah.

So it's a pretty important technology that's all around us that is hitting our eyeballs all of the time. But as usually, we're wondering how many people out there know how LEDs work or what it even stands for, LED. So as usual, Daniel went out into the world and asked people if they knew how an LED works. That's right. And these questions actually predate the coronavirus pandemic. And so these are historical records of in-person interviews back when that was still possible.

Oh, really? Oh, this is an actual on the street interviews. These are from the archive. We haven't had a chance to pull this episode out yet. I see. Do you think people's opinions about LEDs? would have changed by now? Well, people are spending more time inside

under the lights of LEDs. So they have a deeper relationship with LEDs now. Maybe hypnotizes a little bit more since... Yeah, well, you know, people are looking at more screens, and so they have hopefully more affection for LEDs. Yeah, so think about it for a second. If someone asks you how an LED works, would you know what to answer?

Here's what people had to say. No, but I just know it's a better light. Part of me really wants you just say electricity, but isn't it... No, that's fluorescence. Never mind. I was going to say gas, but... That's just fluorescence. The lights?

Yeah. I'm going to assume it's due to a resonance frequency within the LED. I'm not sure. Essentially, it's just a P.N. junction. One side has holes. One side has an excess of electrons. And essentially, transitions in the state of the P.N. junction really slight. So, yeah.

Oh, shoot. Honestly, I don't know I literally don't know Kind of Yeah, yeah, I know Can you explain it to me? Excited atoms But I forgot like

Which atom, like maybe Alien Then excited to a higher state, energy state And when it falls It generates Energy, but yeah That's kind of that idea Isn't that fluorescence?

No similar, but fluorescence is like much weaker energy. So what do you think of these responses? Pretty good. I feel like they fall in line with how I think about LEDs, which is that I don't know much about him. Yeah, I was a little surprised. Some people had no idea. Some people thought they understood it, but we're actually talking about a completely different type of light generation.

That's fluorescence. People got them confused with fluorescent light. Yeah, yeah. And turns out there's lots of different ways to make light. You know, you have incandescent light. We have fluorescent lights, and then we have LED lights. and they all operate on really different physical principles. Yeah, because maybe people got them confused

because I feel like fluorescent lights, I know they've been around for a long time, like neon signs and things like that and fluorescent bulbs, but they sort of made it into people's homes more recently. But then right away, LED sort of came about and then totally replaced them. Yeah, well, fluorescent lights have been around for quite a long time, but yeah, they didn't make it into people's homes until recently

with a compact fluorescence. But there's actually sort of a fascinating legal drama about fluorescent lights because they were first developed pretty soon after incandescent lights, but then General Electric bought up all the patents and prevented anybody from developing or using them and basically kept fluorescent lights out of the market for decades just because they also owned the patents for incandescent lights. So it's sort of a legal political drama that we probably won't even get into today. They're like fluorescence that works with gas. It's not electric. It's on brand with us. So we'll just sit in it. Yeah, they just sort of bought it up and sat on it as a dangerous

technology that they thought would sort of endanger their business. Well, let's get into how LEDs work. But first, let's maybe talk about how some of the other lights that people are familiar with work. So take us back, Daniel. How does a torch work? You know, that's a really awesome question, actually, like, what is fire and how does it work?

And I want to do a whole podcast episode, What is Fire and what is the thing you're seeing that's glowing? Cool. That's going to be lit. It's going to be totally lit. We're going to brighten your life with that one. And remember on our live stream, somebody asked about that, whether fire can have a shadow, which is a totally awesome question. But I think the first light that we should talk about is incandescent lights.

And these are the ones that Edison invented, you know, the ones that people have had in their homes until very recently. It has a little filament in it that glows and eventually it breaks. Right. Yeah, basically what people think of when they think of a light bulb, like a round thing with a little wire through the middle. Yeah, that's your classic light bulb. And all the technologies that we're going to talk about today operate under the same. same essential goal, which is turn electricity into photons. Do you think when Edison had the idea for the light bulb, do you think he had a light bulb over

his head? Was that the only time in history when somebody was actually thinking of a light bulb when they had an idea? Yeah, that's where it comes from, right? That was the first great idea. That was the first idea worthy of having a light bulb over your head. I see. Technically, that's true, yeah.

And so the idea for incandescent lights is to find some material where you can deposit the energy from your electrons and it'll give off light, right? So every one of these strategies, you're going to turn fast-moving electrons into shooting off photons. Photons to the surrounding areas. Yeah. Okay. So how do incandescent lights work? How do light bulbs work? Regular ones? The amazing thing about light bulbs that people probably don't understand is that they glow even when they're off. What? Yeah. Everything glows. It's called black body radiation. Everything in the universe gives off photons, gives off radiation. Even if it's totally black. Even if it's a black hole, Daniel?

Well, technically, yes, black holes do give up radiation. All right. Yeah, no, that's true. I stand corrected. Yes, even black holes have a temperature, right? Everything in the universe that's not an absolute zero glows at some spectrum. Now, usually you don't see it because it's invisible. It glows at very, very long wavelengths, very low frequencies, and so you don't see it.

But this is why, for example, you know, infrared telescopes like the James Webb Space Telescope that looks for infrared light, it sees a lot of noise that you don't even see and have to keep it cold at like negative 50 degrees or whatever. So everything in the universe is already glowed, but it's not so useful, right? What you want is something that glows with light that you can see. A lot, right. Oh, I see. Black body radiation is the infrared.

It's much lower than the infrared, yeah. Most black body radiation, like the cosmic microwave background radiation, is black body radiation from that initial plasma of the universe. And is it like, you know, three degrees Kelvin? It's at very, very long wavelength. But what about something that's at zero degree Kelvin, like absolute zero? Would that still glow? No, something at absolute zero can't glow, but there is nothing in the universe at absolute zero.

So if you're like at 0.001 degrees Kelvin from absolute zero, you would be glowing a little bit. Exactly. And that's why the black hole stuff is actually quite fascinating, because when Stephen Hawking developed his ideas of black holes having a temperature, that automatically suggests that black holes should radiate because like everything else that has a temperature, they should radiate. That's why Hawking's results are sort of black hole thermodynamics because he's thinking about the temperature of black holes and how that connects to how they radiate.

All right, so everything glows in the infrared. So how do we get things to glow in the visible light, the white light spectrum? Yeah, so the spectrum in which you glow depends on your temperature. So really cold stuff glows in the infrared. If you heat something up, then its emissions move into the visible spectrum. So you want to make your filament glow in the visible light instead of in the infrared light, then what you do is you make it hot.

Hotter and hotter. It turned the light from it, not just glows more, but it changes color. It changes color. And that's why, for example, you heat up metal, right? And you see it glows blue, it glows red, it glows white, for example. And the temperature of the metal determines the frequency at which it's glowing, right? Like white hot and red hot are different temperatures of metal, right? And so this is a basic principle. And what's going on in the physics sense? What's going on with the electrons and the atoms? Why is it changing color and how is it giving off the light? So it's always a good idea to try to think about stuff microscopically.

And that's not just because I'm a particle physicist that I think we should always be thinking about the tiny stuff. I think it really does lead to some insight. And so what's happening microscopically when you heat something up is that the electrons inside it, the particles inside it have more ways to move. They're wiggling more. They're bouncing more. So there's just a lot more energy there. Now, the way something glows is when something,

moves from a higher energy level to a lower energy level. You mean like the atoms in it, decay or sort of degrade a little bit or chill out, and when they do that, they emit a photon. Yeah, they're excited. They have some energy stored in them, and that energy comes from, you know, whatever you did to heat up this material, right? Heat means internal energy stored in the motion of these objects. And we had a whole podcast about what temperature means,

and it turns out to be very confusing and amazing, like everything else in the universe. But the way to think about it microscopically is that these atoms are excited. Either the electrons that are whizzing around them have gone up one ladder in the energy level or two ladders or three ladders. Or maybe they're vibrating in new ways or rotating in new ways. These are all ways that they can store energy. The electrons or the atoms? The electrons can move up energy levels, but the atoms also, they can vibrate. Remember, a lot of these are in bonds, right?

Metals are not just free-floating gases. There are these little lattices of things tied together. And they're like, you can imagine little springs between them. And then you can imagine those things vibrating and vibrating in different ways. They have different modes. All right. So they're excited. And so they're giving up energy.

And then they relax because things in the universe don't like to be excited. They like to spread out their energy. And that's why things emit energy because entropy, right? Energy in the universe tends to diffuse. And so if you have it concentrated in one little mode, like one little electron has jumped up three energy levels, it will decay. You'll give that energy off. And the way it does that is by shooting off a photon. And so the more you heat up something up, the more you make all the atoms more

excited, the more photons that are going to come off of this excitement. Exactly. And then the higher the energy of those gaps. So an electron can get pushed up several levels up that ladder. And then it can jump down five levels. And so then the photon has more energy, which corresponds to a higher frequency. So that's how, for example, hot objects can emit in the visible spectrum instead of just at the very, very low energy levels. So the light that they emit has more.

more energy, which is what higher frequency means, which is what visible light means, or invisible light has more energy per photon than infrared light. But I think it also has to be certain kinds of materials, right? Like when I boil water, it doesn't start to glow. I mean, it starts to glow in the infrared, but not in the visible light spectrum. That's an awesome question. How hot would you have to make water in order to make it glow? I don't know the answer to that.

That's a cool question. But you're right. Yeah, everything glows at some level, but not everything can be easily made to glow in the visible. Because I guess it'll melt or burn or boil. Yeah, exactly. Something else will happen to it, turn into vapor. So that's how light bulbs work. It's that they have a little thin wire of metal that you heat up and then that gives us the light. That's right. And the way you heat it up is that you send current through it, right? You send electricity through it. And most of these metals are resistors, meaning that they're not perfect conductors. So the electrons, as they're

trying to go through the metal, are getting bounced into atoms, right? And those atoms are stealing their energy. And this is what heats up something when electricity passes through it. Like, you know, that block that you used to charge your laptop. If you've been charging it for a while, it heats up, right? That's using, that's inefficient. It's using, it's stealing the electricity from those electrons in order to heat up that block. This is how you heat up the filament of tungsten as you pass all this electricity through it. That heats it up and that makes it glow. Right. Yeah. That's a little wire inside of the traditional light bulb. And why tungsten, is it a special kind of metal that can heat up a lot without melting?

Yeah, tungsten just sort of lasts a long time. But these things are really very, very inefficient. Like, it's not a very direct way to get energy into photons, right? You're just heating this thing up, and it's glowing somewhat in the visible, but not always in the visible. And a lot of the energy is just lost. A lot of the energy goes into the infrared, which is useless to us. Yeah, it just goes into making this thing hot, right?

And not all the heat gets turned into visible light. And so only something like 5% of the energy that you put into a light bulb gets turned into light. Wow. Not super efficient. Not super efficient. And also kind of fragile. Like you're baking this thing every single time. So it gets hot and then it gets cold and gets hot and then it gets cold. And you know that like that creates a lot of mechanical stress, which is why these filaments, which are already very, very thin, don't last for that long. So your typical incandescent classic light bulb only works for about a thousand hours. Well, they're making a comeback, you know, in like hip hip restaurants and stuff. Everyone's going for the incandescent bulbs. Yeah, well, the positive thing about incandescent bulbs is they have a very nice glow. Like, it feels like sort of a natural light. You know, the process that produces this light gives you a spread, right?

Not just one color. It's not like a laser beam in your eye. It's a nice spread of warm white light. And so a lot of people like that. It's sort of more similar to sunlight than some of the other technologies we're going to talk about. All right, let's get into some of these other technologies like LED. like fluorescent light bulbs. But first, let's take a quick break.

December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the T.W. U.A. terminal.

Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder. order to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart

Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up.

Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not?

To hear the explosive finale, listen to the OK. Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Imagine that you're on an airplane and all of a sudden you hear this. Attention passengers. The pilot is having an emergency and we need someone, anyone, to land this plane. Think you could do it? It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, do this, pull that, turn this. It's just, I can do my eyes close. I'm Mani.

I'm Noah. This is Devin. And on our new show, No Such Thing, we get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence. Those who lack expertise lack the expertise they need to recognize that they lack expertise. And then, as we try the whole thing out for real.

Wait, what? Oh, that's the run right. I'm looking at this thing. See? Listen to No Such Thing on the IHeart Radio app. Apple Podcasts or wherever you get your podcasts. All right, Daniel, we're talking about how LEDs work and specifically how lights work in general.

So we're going down the list of technologies. And so we talked about incandescent bulbs, which I'm guessing maybe my kids will never have to know how they work technically because everything has sort of moved on. But the next one in the history of light is the fluorescent light bulb. So you were saying these were invented at around the same time as the incandescent light bulb, but they worked on a totally different physics. Yeah, the physics is different.

The idea here is to use excited gas. And, you know, we talked about in the late 1800s, people were making vacuum tubes and, you know, passing currents through it and seeing glows. And that's actually one of the things that led to the discovery of the electron, right? J.J. Thompson discovered the electron by playing with these sort of evacuated tubes and seeing how the gas inside them glows. But then people were playing with other kinds of things and discovered that if you pass a current through a tube that has gas in it,

you can make the gas glow. And the physics here is pretty similar to the physics of incandescent lights, except that you're making a gas glow instead of making like a piece of metal glow. Oh, I see. Instead of a little wire, it's like a tube of gas. Yeah. And you can excite the electrons in that gas. They go up an energy level, and then they jump back down,

and they give off a photon. And I think last time we talked about these, it's sort of related to lightning in a way, kind of. It's almost like you're creating a little bit of lightning in a bottle. Yeah, it's lightning in a bottle. And it's a little bit of plasma, right? In order to pass electricity through a gas, you have to turn it into ions.

You have to tear apart the positive and the negative that usually the gas is made out of and make an ion channel. And, you know, this sounds like Star Trek or whatever, but you're literally making a tube of electrically charged gas. It's like a gaseous wire. It's sort of cool. It's like a gas that conducts electricity, right? And so you're tearing it apart just by creating this electric field from one side to the other.

And then passing that energy through and it excites the gas. It makes the gas glow. Like the atoms of the gas inside are now giving off. They're like absorbing these electrons that are going through and then they give them off as photon. That's right. The microphysics of what's happening is that these electrons, the current that's passing through will sometimes bump into an electron in the gas atom. and bump it up a few energy levels and then it'll fall back down

and when it does that it gives off a photon so you're turning the kinetic energy of some initial electron into an excited state of the atomic electron which then emits a photon so that's how you get the energy

from the electron into a photon and it's kind of a binary process right like it's hard to dim a fluorescent light bulb right like a little regular bulb you can do that but a fluorescent you know it's either on and off and if it's sort of on the edge you'll blink

can kind of give you eye strength. That's right, because you need to create this plasma. You need to like ramp it up to a high enough voltage so that you can create this ion channel and the whole thing starts up. It's almost like starting up a little fusion reactor inside. Oh my God. It's sort of awesome, yeah. Suddenly fluorescent lightballs are way cool.

They're lightning in a bottle and fusion bombs in a tube. Yeah. And the cool thing about them is that they're a lot more efficient. Doing this with a gas like a mercury vapor, which is what's typically used, is something like 20% efficient instead of like the 5% of your incandescent light bulb. Where does the other 78% efficiency go into heat as well? But they don't get that as hot. That's exactly right.

They don't get as hot, which is why they're more efficient, right? So more the energy goes into creating light and less of it goes into like heating up the actual apparatus. So I think that all makes sense. One interesting facet, which I thought was cool, was that the best thing to use to make this light is mercury vapor

because you don't need really high voltage and it's one of the most efficient ways to do it. But mercury is like, super poisonous, which is, which makes it like, it's a bad idea. Also, mercury gives off light. It's not visible. It gives off ultraviolet light. Oh, my goodness.

It poisons you and gives you cancer at the same time. No, but that's why a lot of these fluorescent light bulbs are not clear. They're frosted because the inner side of the glass contains another material, which absorbs the ultraviolet light, uses some of the energy, and then gives off light in the visible. So it's like a two-step process. The mercury vapor gives off UV photons, which are then like stepped down into the visible light by some phosphorescent coating inside the bulb. Wow.

It's a lot to it. Yeah, it's a complicated thing. And, you know, you have to create this plasma. And that's why fluorescent light bulbs until recently, not as commonly used in the home. They're more expensive and more complicated. But they're a lot more efficient, like 20% instead of 5%. And they work for like 10,000 hours instead of 1,000 hours. And the light is kind of different, too.

It's wider, generally. It's wider, yeah. And it kind of drives me bonkers. Like, I don't like the light from fluorescent light bulbs. It makes me feel like I'm, you know, in a target or in like an alien autopsy examination room. What? Target and alien autopsy. That's where your mind goes.

It's worse case scenarios. Well, actually, now that I think about it, I'd love to be in an alien autopsy. Yeah, or Target for that, to be honest. It's just that I don't know why the lighting in alien autopsy, scenes in science fiction is always so terrible. Like, why do they always use the horrible fluorescent flickering lights? I see. Well, it's just so that the green comes out of their skin more, you know?

Makes their green skin seem lovelier. I see. The aliens agent insisted that they have it that way is in their contract. All right. Brown M&Ms and fluorescent lights, please. That's right. That's right. And a butt, though.

I didn't think that would make you laugh so much, Daniel. I don't think aliens are. so vain, all right? Well, hopefully not. But yeah, so that's incandescent and fluorescent lights. And so let's get into the topic of the podcast, which is how LED lights work. And these are pretty recent. I feel like in the last 10 years, they've become more popular. And they're also sort of everywhere, right? They're in phones. They're in TVs. They're pretty much every kind of screen. Even on people's watches now, I have LEDs. And so first of all, Daniel, what does LED stand for? It stands for light emitting diode.

Light emitting is obvious, right, giving off light. And diode is this little physical thing that was invented in the 50s and 60s that's made out of semiconductors. And that's really the core idea here is that instead of using a hot little tube of metal or a hot tube of gas, let's see if we can build this thing out of semiconductors. And semiconductors are what computer chips are made out of, right? I mean, that's what computers are made out of. So this is kind of like they adapted that technology, or they figured out they can also use it to emit light? They can also use to emit light. And you're right, semiconductors are incredible.

Also the basis of transistors, which is how we build computer chips. One of the cool things about semiconductors is that we can print them really finely. We can construct super tiny circuits that have really specific semiconductors using lithography. And that's how we make computer chips so small. We can make LEDs really small. But first, maybe we should talk about what a semiconductor is. It's not somebody who's driving a semi, for example. Or someone who's driving with one eye closed.

Or conducting an orchestra, but only half the time. Yeah, looking at their phone. And to understand a semiconductor, you have to understand where it falls sort of between other objects, like an insulator and a conductor. It's basically like a conductor that you can control, right? Like it's a resistor, but you can also shut it off if you give it a different signal. Sort of, yeah. I think if it's sort of like a combination between an insulator and a conductor.

Because in an insulator, electrons cannot jump between atoms. Like, one atom has its electrons, and the other one has its electrons. And the electrons just stay in their atom. They have a little localized little neighborhood that they hang out in. But in a conductor, the electrons flow freely. Like, they don't necessarily have an assignment. They don't have like a home address. They just sort of like move around between atoms.

It doesn't take much energy to go from one atom to the next. There's no, you know, barrier there. It insulates. You can't conduct electricity. Yeah, so insulators, electrons can't. jump between atoms and in a conductor electrons just flow very easily between atoms. Now, in a semiconductor has both, right? It has, there's a flow zone and a no flow zone. So if you have enough energy, then you can get up into this conduction band where you can

like float around between the atoms. So high energy electrons can jump between them, but low energy electrons are sort of stuck in their atom. So there's like the cool kids that are running all over the neighborhood and then the ones where their parents tell them they have to stay home. They're all mixed together. Yeah, and there's two different kinds. And so based on how much energy you have. And so that's what we call this band gap. There's this energy gap.

If you're above a certain energy, then you can move around. And below that, you can't move around. So that's what a semiconductor is. And it's fascinating because it has this band gap. And as you said, if you excite the electrons, you can turn it into a conductor. But some of the electrons, they're low enough energy, then they're an insulator. So you get this sort of fine-grained control about the electrical flow, which is what makes it good for building circuits,

and all sorts of stuff. Right, but it's not a question of the energy of the electrons, right? It's more of a question of the kind of the energy of the medium, of the material. Yeah, the material determines sort of this structure, right? Different kinds of semiconductors have different size band gaps, but that band gap is the energy of the electrons that we're talking about. And you can build all sorts of different kinds of semiconductors, and you can build semiconductors based on like what material you use, like is it gallium, is it silicon, is it some

combination of these two? You can build semiconductors that have a bunch of extra electrons in them. So that's called P-type, like there's a bunch of extra electrons floating around. Or there's semiconductors that are called N-type that have like empty holes where electrons should go. Yeah. So they're both semiconductors. They're both about usually mean out of silicon, right, with some sort of metal kind of infused in it. Yeah.

And so you often start with silicon and then you add little bits of other stuff to make different kinds. And a diode is just an N-type semiconductor right next to a. P-type semiconductor. And what this means is very simple. It just means that the electricity can flow in one direction. That's what a diode does. So the P-type has a bunch of electrons, and the N-type has a bunch of holes for those electrons to fall into. So the P-type one has electrons floating above this band gap. They can move around, et cetera, et cetera. When you put a current over, they just fall into the holes. And electrons jumping from high-energy states to low-energy states is how you emit energy. So when they do that, they release photons. So a diode is just P-type and N-type stuck

together, and a light-emitting diode is one where when the electrons fall in, they emit visible light. And it has to be a special kind of material, or is it still just silicon with some kind of metal in it? It has to be a special kind of material to get the right color light. And so that's really the key. That's the core physics for why blue LEDs were so fascinating. The first LEDs people invented, this gap was kind of small. sort of hard to make it work. And so when they fell from P-type to N-type, they didn't have that much energy

and they emitted mostly in the infrared. And if, for example, the LED that's in your remote control, the one that controls your TV, you don't see light coming out of the top of the remote control because it comes out in a wavelength you can't see. It comes out as infrared light to talk to your TV. But there's an infrared LED at the top of your remote control. And those were the first ones that were invented.

It was actually back in the 60s that they first came out with infrared LEDs. And then the challenge was coming up with different kinds of material to negotiate this like P type, N type difference. So you've got a larger gap. So you have more energy when they fell. So you have more energy in the photons so they could be visible light. Oh. So it's all about the difference between the P and the N types of materials.

Yes. Okay. So it sort of depends more on the N type and the size of the hole. No, the hole is just a hole for an electron. It depends on the gap between the P type and the N type. So you're right. depends on the type of material and the size of this gap. And you're putting this P-type and this N-type next to each other.

And it's basically how far they fall. Like, are they just stepping down from the curb and they go, oops, and they just give off a little bit of light? Or are they jumping down Niagara Falls and screaming all the way down and giving off a lot of energy? Oh, I see. The electrons go from the P-type to the N-type. They jump.

Yeah. I see. Yeah. They jump where they fall, you know, depending on whether you believe the electrons can make decisions, man. They're pushed. They're more like pulled, right? Yeah, they're more like pulled. And so basically, an LED is a bunch of electrons screaming.

Great. Next time you look at your phone, your phone is screaming. They are screaming and screaming photons at you. Every time, yeah. It's not just your brain that's screaming from your Twitter feed. And the thing that's amazing about this is that it's solid state, right? Nothing is moving here. You don't have gas that's bouncing around.

You don't have metal that's heating up and cooling down. It's just fixed. And it's just like an electrical circuit. And that makes it last for a very, very long. long time. It lasts for like 100,000 hours before it finally breaks. Electrons can scream for as long as you need them to, that's what you're saying. That's right. Unfortunately, the lifespan of electron is very, very long. It's doomed to a long life of falling down this gap. I guess my question is, what keeps the light going? Like,

once it falls into the hole, wouldn't it just stay in the hole? Yeah, it does. Wouldn't it fill up all the holes? Well, you have a current, right? And so you're pulling these electrons out of the end type. So the whole thing is connected to a current. Imagine like a battery, power the LED, it's sending fresh electrons into the P-type and pulling the electrons out of the end time. So the whole thing is a circuit. It is like a waterfall. It's like a continual waterfall. Exactly. It's just like a waterfall. You're pumping on one side and then they scream on their way down. It's more like a roller coaster because of the screaming. I see. Yeah, that's right. Because then they go down and then the card gets pulled over and then

up the ramp again and then down and then screen. Let's not think of it as electron suffering, but electrons is having a lot of fun. And you might wonder, why do people go on roller coasters because they scream the whole time? Well, I guess they like to scream. And so we can imagine that also electrons are enjoying this ride. There you go. They're thrill seekers. And they seem to be happy to do it because LEDs last for 100,000 hours.

And it's very, very efficient. Most of the energy that you're sending into this circuit actually goes into emitting light. Yeah. It's like more than 50% of the energy. Wow. That's 10 times. 10 times more efficient than incandescent bulb. Yeah, 10 times more efficient.

And the challenge is in finding the right gap. So you get the right energy level. So you get the right colors. And so the first thing was infrared. And then infrared is the lowest frequency, the longest wavelength. And then they figured out ways to make them longer so they were visible. And then longer. So you got red.

You got green. And then the challenge was blue LEDs. All right. Let's get into the amazing discovery that was discovering blue LEDs and why I got the Nobel Prize. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed.

There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop.

Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't. trust her. Now he's insisting we get to know each other, but I just want her gone. Now hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person,

this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio about Apple Podcasts or wherever you get your podcast. Imagine that you're on an airplane and all of a sudden you hear this. Attention passengers.

The pilot is having an emergency and we need someone, anyone to land this plane. Think you could do it? It turns out that nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, do this, pull that, turn this. It's just, I can do my eyes close. I'm Mani. I'm Noah.

This is Devin. And on our new show, No Such Thing, we get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence. Those who lack expertise lack the expertise they need to recognize that they lack expertise. And then, as we try the whole thing out for real. Wait, what? Oh, that's the run right. I'm looking at this thing.

Listen to No Such Thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. All right, Daniel, somebody got a noble prize for discovering the blue LED. So what's so special about blue LEDs? I like the way you make it sound like they discovered a blue LED. Like, well, I was sweeping up in my lab and I found this thing on the ground. Oh, my God, it's a blue LED, right? It's just what I was looking for.

Because that's how we discover particles, right? You know, we're like, oh my gosh, look, I found a tau particle, and now I get a Nobel Prize. I didn't, like, design it or engineer it or invent it, right? Should be more like somebody designed blue LED, invented. Yeah, somebody invented the blue LED, which is sort of awesome and impressive. So we couldn't just take a white LED and put a blue filter on it? Well, that's the thing. You can't make white LEDs without blue, right?

Before we had blue LEDs, we had green and we had red, and so you couldn't make white LEDs. That's why blue LEDs are so important, because, you can't make white LEDs. are so important because with blue, you can make the combination. You need to make white. And nobody wants in their reading light a green light or a red light. You want a white LED. And you couldn't make white without blue. Oh, you need the blue. You need the blue to make the white. Yes, you need the blue to make the white. And that's why LEDs have exploded in applications everywhere because now they can make essentially any color because we have the missing blue. Cool. So tell me what was so hard about it and what's the physics behind it. Yeah. And so it's sort of an

interesting question. Like, it really was an engineering puzzle. Like, you just needed to get the right material. You needed to get the right material with the right thickness and configure it all correctly to get blue. And it's tricky to get this gap to be extra, extra large, large enough to make so that when the electrons go down that roller coaster, they scream for long enough to give you a blue photon. And, you know, it turns out to be something of a condensed matter and solid state engineering problem. And a couple of Japanese people figured it out. You need some mixture of gallium nitride with other silicon substrates and then you can get this blue LED but i guess why was it so hard like when you try to make electrons jump that much it would burn out or they just wouldn't

do it or you know they wouldn't scream as much as you wanted them what was the difficulty in getting this right it was just in finding one that would work you know most things just didn't have this large enough gap and so it's just about finding a material that had this gap and that also worked yeah that also worked i mean you can make a gap but it may not necessarily work Yeah, to get the electrons to flow across it. And so we can't necessarily predict in advance whether something's going to work. So they sort of had just had to search through lots of different kinds of materials and try this and try this and have insight and inspiration and also just some luck in making it work. And so that's why I think it's interesting like, does this deserve a physics Nobel Prize?

Like there's no new principle discovered here. There's no fundamental revelation of the nature of the universe or space time or history or whatever. It was an engineering step forward, which, hey, deep respect for the engineering step forward. But I think the reason it got the physics Nobel Prize is because of the huge impact on society. Really? You guys look down on things that are useful. You're like, well, you know, I think the original Nobel Prize was supposed to be about things that shaped society. And so I think Alfred Nobel would probably be pretty pleased. But more recently, a lot of these prizes have been awarded for, like, deep but maybe impractical discoveries about the nature of neutrinos or gravitational waves.

Oh, I see. That's right. Nobel was an inventor, right? He wasn't a physicist. He was an engineer. Exactly. You guys have co-opted our prize. Exactly.

So in some sense, this is like a return to Nobel's roots, right? It's recognizing something of great import to society because it has had a huge impact. Right. It was like the missing piece. There's nothing weird physically about blue. It's just sort of the highest frequency and therefore the last for us to put together. Oh, I see. So do you think somebody should have gotten a prize, a noble prize for discovering the Higgs boson?

Because the people who won it won it for coming up sort of with the Higgs boson. But the people who discovered it, it was mostly just sort of engineering, right? You just described my whole field as mostly sort of just engineering, which is so many fascinating angles, because I think you meant that as a diss, but you described as engineering. Oh, no. Oh, I hold engineering at the highest esteem, Daniel. I was actually trying to pay you a compliment. You were trying to elevate our field by describing it as engineering.

I appreciate that. It's aspiring to be useful. Well, I'm not even sure how useful it is to have discovered the Higgs boson. But I think the great innovation there was definitely in having the idea and finding it, I don't know how many big steps forward. I mean, it's a huge effort and technological achievement. But I don't know that we necessarily created anything new. We certainly didn't make anything as fascinating and impactful as the blue LED.

We just sort of confirmed an idea that it was in people's minds. So we revealed something about the nature of the universe, but something that sort of had been suspected to exist already. Okay, so back to the blue LED. That's important because now you have blue, and with red and green, you can make white light. So you can make any kind of color now that you have blue LEDs. Yes, exactly.

And so these guys invented it in the 90s, and then they won the Nobel Prize for it, a few years later, that's how LEDs work, and that's why they're so important. So did the people who discover the red LEDs and the green LEDs also get a prize, or only the one who waited until the end and procrastinated to discover the missing color, get the prize? I feel like you have another horse in this race here. You're pro procrastination. Yeah, I build a whole career on it, Danny.

Yeah, the lesson here is wait and just sort of put the period at the end of the sentence, and you'll get the prize for everybody else's work. Yeah, there you go. But in a way, it's true, right? Like, the person who discovered the red and the green one didn't get a prize. But somehow, like, you know, completing the triangle to get white light made a bigger splash. Yeah, the person who puts the capstone on the top of the pyramid, right, is the one that claims the prize. Right.

The one who discovers the mass particles is the one who. But yeah, so now we can make white light with LEDs that is super efficient and also small, really small. Like maybe before you couldn't make incandescent bulbs small enough for, you know, retinaught display kinds of screens. but now you can because LEDs, you can make them really, really small. Yeah, because we can print semiconductor is using these lithography techniques to be really, really super tiny. And, you know, we invented these techniques mostly so we can make transistors really, really small, so we can make computer chips packed with all sorts of little circuits on them,

but we can also use the same technology to make LEDs. And LEDs, remember, are not monochromatic. They're not like tiny little lasers, right? Lasers shoot exactly one frequency or very, very tight band of frequency, because the photons come from one atomic step. LEDs are not quite like that. The light they emit is narrowly focused. It doesn't have just a single wavelength or frequency.

It is a little bit like incandescent that it's kind of broad. Yeah. Yeah, they're broader than lasers, but not as broad as incandescent. So that's why they're a specific color, but they're not like a really tight band like lasers. Okay. So then when I turn on the flashlight on my phone and I see this white light come off

and that helps me at night and get around at night, I'm actually seeing not a white LED, but like a whole bunch of red, blue, and green LEDs mixed together. That's right. And when you look on your screen and you see white for the blank page and the word document of the novel you've been writing for 10 years, then what you're really seeing are red, green, and blue blinking your failure actually. Blinking. But, you know, that's what Newton discovered is that white light is actually just a mixture of colored lights. There's no difference. There is no white photon. There's no color in the spectrum that is white. A white light is just a mixture. of red, green, and blue. Wow. And so basically that

increased our human level global efficiency for light by 10 times. So now we can be a whole lot more eco-friendly. Yeah, except probably just means we made a lot more bulbs. So we're probably using the same electricity and now we're just lighting everything up. What? No, I changed

all the light bulbs in my house for LEDs and boy, your power bill drops like crazy. Yeah, well, do you appreciate it though for working? Like when you're drawing something? Do you like using natural light or incandescent light or LED light? Or does it not make any difference because you do everything at 2 a.m.? Well, I draw everything on the computer. So it's all LED powered, baby, you know? Yeah, I guess so. All right. Well, that's pretty cool. I have a new respect for blue LEDs now and also a little respect for red and green LEDs. You know, I feel like

they got the short end of the color triangle. They are singing the Nobel Blues. All right, but I think it points us to how even a small discovering physics or experimental physics can lead to basically a revolution in how we lead our lives and what kinds of devices we use every day. That's right. Engineering can change the world.

What? Can you guys replay that? Which is one more time. I just want to make sure that we heard it right. Can you replay it? Engineering can change the world. I'm going to download it, frame it on an LED frame. I should send you a little

button. You can just press that and hear me say that every time you want. I'm going to hack into your phone and make it your ringtone. That's your new ringtone. All right. Well, we hope you enjoyed that. And we hope you look at light in a whole different light. Thanks for tuning in. See you next time. Visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. Ah, come on, why is this taking so long? This thing is ancient. Still using yesterday's tech, upgrade to the ThinkPad X1 Carbon,

ultra-light, ultra-powerful, and built for serious productivity. With Intel core ultra-processors, blazing speed, and AI-powered performance, it keeps up with your business, not the other way. around. Whoa, this thing moves. Stop hitting snooze on new tech. Win the tech search at Lenovo.com. Lenovo, Lenovo.

Unlock AI experiences with the ThinkPad X1 Carbon, powered by Intel Core Ultra processors, so you can work, create, and boost productivity all on one device. December 29th, 1975, LaGuardia Airport. The holiday rush. Parents hauling luggage. kids gripping their new Christmas toys. Then everything changed. There's been a bombing at the TWA terminal.

Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot.

He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.